The present invention relates to an ultrasonic transducer used in a device for detecting obstacles ahead or behind a vehicle.
Recently, an obstacle detecting device for guarding the backward movement of a vehicle, which employs an ultrasonic transducer, has been proposed.
In the obstacle detecting device, the ultrasonic transducer is installed in the rear of the vehicle, especially in a rear bumper thereof. The ultrasonic transducer transmits ultrasonic waves behind the vehicle and receives the ultrasonic waves reflected from an obstacle to which the rear of the vehicle approaches and of which a driver does not become aware. Then, the obstacle detecting circuit detects the distance between the vehicle and the obstacle by measuring the time taken until the reflected waves return from the obstacle.
The ultrasonic transducer used in the above described obstacle detecting device comprises an ultrasonic vibrator, and a reflecting in a horizontal direction plate for reflecting the ultrasonic waves emitted by the ultrasonic vibrator.
The ultrasonic transducer as described above is generally installed at a position near a road surface so that spattered muddy water or the like is liable to adhere to the ultrasonic vibrator and the reflecting plate, resulting in the lowering of the function of the ultrasonic transducer.
In order to prevent the spattered water or the like from adhering to the ultrasonic transducer, an attempt has been made to mount the ultrasonic vibrator and the reflecting plate within a cylindrical housing opening backward. However, this configuration has the following problem. Namely, one portion of the transmitted ultrasonic waves is reflected by a cylindrical wall of the housing and is fed out of the housing in a direction toward the road surface. Then, after being reflected by an object on the road surface, for example a tire stopping stone, the ultrasonic waves return to the housing and are repeatedly reflected by the cylindrical wall thereof to reach the ultrasonic vibrator. As a result, the obstacle detecting circuit misdetects an object on the road, for example a tire stopping stone, against which the rear of the vehicle does not collide, as an obstacle to be detected.